Lift force coupling propelling structure for semi-annular empennage aircraft

Abstract

According to the lift coupling propelling structure for the semi-annular empennage aircraft, propelling propellers are arranged at the tail end of a fuselage of the aircraft, connecting rods are arranged below wings, and lift propellers are arranged at the front ends and the rear ends of the connecting rods; the tail end of the rear part of the connecting rod is connected with a semi-annular empennage; the minimum vertical height L from the highest point of the front edge of the semi-annular empennage to the tip of the propelling propeller is equal to 0.1-0.2 time of the radius R of the tip of the propelling propeller; the maximum included angle alpha of the overlapped area of the rotating contour of the lift propeller and the outer contour of the front fuselage is 45 + / -5 degrees; the maximum included angle beta of the overlapped area of the rotating contour of the lift propeller and the outer contour of the rear fuselage and the outer contour of the rear edge of the wing is 90 + / -5 degrees. According to the lifting force coupling propelling structure special for the semi-annular empennage, by optimizing the coupling relation between the propelling propeller and the semi-annular empennage and the coupling relation between the lifting force propeller and the fuselage wings, the propelling efficiency of the propelling propeller can be remarkably improved, and the lifting force loss of the lifting force propeller is reduced.

Description

Technical Field

[0001] This invention relates to the design of lift and propulsion structures for vertical takeoff and landing aircraft, and particularly to a design of a coupling structure for lift and thrust for an aircraft with a semi-circular tail fin, especially a lift-coupled propulsion structure for a semi-circular tail fin aircraft. Background Technology

[0002] Vertical takeoff and landing (VTOL) aircraft do not rely on runways and can take off and land directly in confined areas such as city rooftops, ship decks, or complex terrain, possessing hovering and low-speed precision maneuvering capabilities.

[0003] CN 114852324 B discloses an aircraft with a fixed wing and a vertical takeoff and landing (VTOL) lift propeller, with a propeller located at the tail of the fuselage. In this prior art, the lift propeller is supported by a support beam under the wing, which also supports the yaw surface of the tail fin. The horizontal tail fin is supported between the tail of the fuselage and the support beam. In VTOL mode, the lift propeller is close to the fuselage, causing interference and strong downwash, which can lead to insufficient lift. During the transition from VTOL to cruise, the aerodynamic separation of the lift propeller intensifies under the influence of the horizontal airflow, reducing its efficiency. If the fixed wing has not reached maximum lift during this transition, the reduced efficiency of the lift propeller under the influence of the horizontal airflow can easily lead to a crash due to a sudden drop in lift. To compensate for insufficient lift, this prior art uses two layers of lift propellers, increasing system complexity and structural weight.

[0004] In addition, the tail structure of this prior art is located on the front side of the propeller, which may generate additional aerodynamic interference with the propeller in some flight states, making it difficult to achieve high coupling propulsion efficiency.

[0005] For example, US 5242132 A discloses a multihull-type V-STOL aircraft employing an integrally articulated curved tail and a mid-fuselage ducted thruster with tilt-angle capability. The curved tail achieves triaxial compound deflection via a hinge connected to the fuselage, aiming to reduce drag and weight using a single structure. However, this unconventional curved tail structure suffers from complex actuation control and an excessively heavy drive system. When isolated from the thruster, it cannot provide additional propulsion efficiency, thus rendering this curved tail design as a substitute for a traditional tail impractical. Furthermore, the tilt-angle ducted thruster structure is complex, and it also suffers from a sudden drop in lift under horizontal airflow during the transition from vertical to level flight.

[0006] In the twin-fuselage amphibious aircraft disclosed in US 6592073 B1, the tail control surfaces are integrated into the ducted propulsion housing. The torque of the tail control surfaces is limited by the size of the duct, resulting in insufficient maneuverability and sluggish aerodynamic response at high angles of attack or engine failure. The propeller is entirely encased in a fairing, and the propeller wake disturbs the control surfaces at close range, causing nonlinear control responses (such as yaw-induced unintended pitch). The airflow between the propulsion and control surfaces interferes with each other, and the deflection of the control surfaces disturbs the inflow to the propulsion, reducing the aircraft's propulsion efficiency.

[0007] In the annular tail section disclosed in WO 2008 / 081098 A1, because the propeller is enclosed by the annular tail section and the fuselage, the propeller wake will directly impact the inner wall of the annular section, which can easily induce turbulence, causing a sharp drop in rudder effectiveness at high angles of attack and making yaw control prone to coupling with roll loss of control. While using a ducted propeller can isolate the interference between the propeller and the tail section, it also loses the significance of the coupling design between the tail section and the propeller.

[0008] In summary, existing vertical takeoff and landing (VTOL) aircraft suffer from insufficient lift and a sharp drop in lift during transitions. Furthermore, the interference of the tail structure with the propulsion system in existing technologies also limits the improvement of propulsion efficiency. Therefore, for VTOL aircraft, a coupled design approach is needed to enhance both lift and propulsion efficiency comprehensively. Summary of the Invention

[0009] The technical problem to be solved by the present invention is to provide a lift-coupled propulsion structure for a semi-annular tail fin aircraft to reduce or avoid the problems mentioned above.

[0010] To address the aforementioned technical problems, this invention proposes a lift-coupled propulsion structure for a semi-annular tail fin aircraft. The semi-annular tail fin aircraft includes a fuselage, wings, and a propulsion propeller located at the tail end of the fuselage. A connecting rod parallel to the fuselage axis is disposed below each wing on both sides of the fuselage, with a lift propeller at each end of the connecting rod. A semi-annular tail fin is connected to the rear ends of the two connecting rods. The semi-annular tail fin originates from the rear ends of the connecting rods and extends upwards along an arc-shaped path to form a downward-opening semi-annular aerodynamic structure. The leading edge of the semi-annular tail fin reaches its highest point... The point is located in the vertical plane of the fuselage longitudinal axis. The minimum vertical height L of the highest point of the leading edge of the semi-annular tail fin from the tip of the propeller is equal to 0.1-0.2 times the tip radius R of the propeller. The maximum angle α between the rotational profile of the lift propeller at the front end of the connecting rod and the outer profile of the forward fuselage on the vertical projection plane is 45±5 degrees relative to the rotation center of the lift propeller. The maximum angle β between the rotational profile of the lift propeller at the rear end of the connecting rod and the outer profile of the rear fuselage and the trailing edge of the wing on the vertical projection plane is 90±5 degrees relative to the rotation center of the lift propeller.

[0011] Preferably, the leading edge of the semi-annular tail fin has a swept-back configuration, and the horizontal distance C1 at which the highest point of the leading edge of the semi-annular tail fin exceeds the end of the aircraft tail is equal to 0.5-0.8 times the chord length C0 of the tail fin airfoil section.

[0012] Preferably, the installation angle γ of the lifting propeller is tilted inward by 3-5 degrees relative to the longitudinal vertical plane of the fuselage.

[0013] Preferably, the minimum vertical height between the disk surface of the lifting propeller located at the front end of the connecting rod and the lip line of the forward fuselage is H1, where H1 < R / 4, and R is the diameter of the lifting propeller.

[0014] Preferably, the minimum vertical distance between the disk surface of the lifting propeller located at the rear end of the connecting rod and the trailing edge of the wing is H2, where H1 < R / 4, and R is the diameter of the lifting propeller.

[0015] Preferably, the radius at a position 0.6-0.7 times the tip radius R of the propeller is R1, the vertical highest point of the tip radius R is the intersection of the horizontal projection of the leading edge of the semi-annular tail fin with P1, the vertical highest point of the radius R1 is the intersection of the horizontal projection of the leading edge of the semi-annular tail fin with P2, the distance from the propeller disk surface to point P1 is D1, the distance from the propeller disk surface to point P2 is D2, and the difference between D2 and D1 is equal to 0.1-0.5 times the radius R.

[0016] Preferably, the leading edge of the semi-annular tail fin has a sweep angle of 25-50 degrees relative to the horizontal plane passing through the longitudinal axis of the fuselage.

[0017] This invention proposes a lift-coupled propulsion structure specifically for a semi-annular tail fin. By optimizing the coupling relationship between the propulsion propeller and the semi-annular tail fin, as well as between the lift propeller and the fuselage / wing, the propulsion efficiency of the propeller can be significantly improved, the lift loss of the lift propeller can be reduced, and the time of sudden lift drop can be delayed, while leveraging the structural advantages of the semi-annular tail fin. For example, by setting the propeller as a whole at the leading edge of the semi-annular tail fin, and limiting the distance of the semi-annular tail fin beyond the propeller propeller to a certain range, higher propulsion efficiency can be achieved. By designing a coupling region between the lift propeller and the blended wing-body, the rotational profile of the lift propeller, which is most affected by the wing-body, is shielded below the fuselage and wing, thereby shielding the propeller tip to weaken the tip vortex and further reduce lift loss.

[0018] In addition, the aircraft of this invention adopts a fixed-wing tail propulsion layout, which can fly horizontally like a conventional aircraft or take off and land vertically. The semi-circular tail structure at the rear of the fuselage eliminates the lower closed frame, which has a significant weight reduction advantage. Furthermore, the open lower structure and the swept-back configuration that extends beyond the tail end of the aircraft effectively avoid the obstruction of the control airflow by the fuselage tail structure, thus avoiding the problem of control surface failure at high angles of attack. At the same time, the open lower structure also facilitates maintenance of the fuselage and engine below the tail. Attached Figure Description

[0019] The accompanying drawings are intended only to illustrate and explain this application and do not limit the scope of the invention.

[0020] Figure 1 This is a top view schematic diagram of an aircraft with a semi-circular tail fin according to a specific embodiment of the present invention.

[0021] Figure 2 This is a bottom-view schematic diagram of an aircraft with a semi-circular tail fin according to another specific embodiment of the present invention.

[0022] Figure 3 The image shown is a bottom view of a lift-coupled propulsion structure for a semi-circular tailed aircraft according to a specific embodiment of the present invention.

[0023] Figure 4 The image shown is a front view of a lift-coupled propulsion structure for a semi-circular tailed aircraft, according to another specific embodiment of the present invention.

[0024] Figure 5 The image shown is a structural side view of the nose section of a lift-coupled propulsion structure for a semi-circular tailed aircraft, according to another specific embodiment of the present invention.

[0025] Figure 6 The image shown is a structural side view of the tail section of a lift-coupled propulsion structure for a semi-circular tailed aircraft, according to another specific embodiment of the present invention.

[0026] Figure 7 The diagram shown is a partial side view of a lift-coupled propulsion structure according to another specific embodiment of the present invention.

[0027] Figure 8 This diagram shows a comparison of the horizontal projection relationship between the rear and side views of the lift-coupled propulsion structure according to another specific embodiment of the present invention. Detailed Implementation

[0028] To provide a clearer understanding of the technical features, objectives, and effects of the present invention, specific embodiments are now described with reference to the accompanying drawings. Identical components are denoted by the same reference numerals.

[0029] like Figure 1-2 As shown, this invention proposes a semi-circular tail fin aircraft, which has a semi-circular tail fin 1 at its tail. Specifically, as shown in the figure, the semi-circular tail fin aircraft of this invention has a fuselage, wings, and a propeller 3 located at the tail end of the fuselage, similar to a conventional fixed-wing aircraft. A connecting rod 13 parallel to the fuselage axis is located below each wing on both sides of the fuselage, and a lift propeller 5 is located at each end of the connecting rod 13. This invention's aircraft adopts a fixed-wing tail propulsion layout, allowing it to fly horizontally like a conventional aircraft as well as take off and land vertically.

[0030] Unlike conventional and existing tail designs mentioned in the background section, the present invention connects a semi-circular tail 1 from the rear ends of two connecting rods 13. The semi-circular tail 1 is not connected to the fuselage as in the prior art. Instead, it starts from the rear ends of the connecting rods 13 and extends upward along an arc path to form a downward-facing semi-circular aerodynamic structure. The highest point of its arc extension is located behind the tail end of the aircraft, and its leading edge 12 is swept back.

[0031] The semi-circular tail fin of this invention adopts a semi-circular open structure, which has a significant weight reduction advantage compared to existing technologies. The semi-circular tail fin extends upward from below the wing, and the high-speed airflow on the upper surface of the fuselage avoids the connection area of ​​the semi-circular tail fin, thus preventing airflow from interfering with the aerodynamic shape of the tail fin. Furthermore, the open structure at the bottom of the semi-circular tail fin and the swept-back configuration that extends beyond the tail end of the aircraft effectively prevent the tail structure of the fuselage from obstructing the control airflow at high angles of attack, avoiding the problem of control surface failure at high angles of attack. At the same time, since the tail fin structure does not obstruct the tail of the fuselage, it also facilitates maintenance of the fuselage and engine below the tail fin.

[0032] In one specific embodiment, the starting end of the semi-annular tail fin is rigidly fixed to the underside of the wing via a connecting rod 13. The connecting rod 13 is a double rod structure symmetrically arranged under the wings on both sides, and the double rods are spaced a distance from the fuselage sidewall to avoid turbulence interference from the fuselage.

[0033] In one specific embodiment, for example, a semi-circular tail fin (airfoil: NACA 0012) can be manufactured using carbon fiber composite material. The semi-circular tail fin originates from the connecting rod 13 located 15-50 cm below the fuselage below the wing. The tail fin extends upward along an arc-shaped path, and the horizontal distance C1 at which the highest point of the leading edge of the semi-circular tail fin exceeds the tail tip of the aircraft is 0.5-0.8 times the chord length C0 of the tail fin's airfoil section (e.g., ...). Figure 7 As shown), the sweep angle of its leading edge relative to the horizontal plane passing through the longitudinal axis of the fuselage is 25-50 degrees. Two titanium alloy connecting rods (10-15cm in diameter) rigidly fix the starting end of the tail fin to the lower surface of the wing, with the rods spaced 0.5-0.8m from the fuselage sidewall (to avoid the turbulence zone of the fuselage).

[0034] Furthermore, in the specific embodiment shown in the figure, a propeller is installed at the tail end of the aircraft, and the propeller disk plane of the propeller 3 and the semi-annular tail fin 1 are arranged at intervals to avoid spatial interference.

[0035] Furthermore, in one specific embodiment, except for the area where the semi-annular tail fin 1 is connected to the connecting rod 13, the airfoil section of the semi-annular tail fin remains consistent along the arc-shaped extension path to ensure the continuity of the aerodynamic shape and optimize the flow field, while reducing manufacturing difficulty.

[0036] Furthermore, in one specific embodiment, the trailing edge of the semi-annular tail fin is provided with three independent deflection surfaces, each of which is controlled by an actuator via fly-by-wire.

[0037] Specifically, as shown in the figure, the control surface includes a central control surface 14 and two lateral control surfaces 15, which are distributed circumferentially along the trailing edge of the semi-circular tail fin.

[0038] More specifically, the central control surface 14 is symmetrically arranged along the longitudinal axis of the aircraft and is used for pitch control; the lateral control surfaces 15 are symmetrically arranged on both sides of the central control surface 14 in an inclined manner, and when the two deflect synchronously, they mainly control yaw, and when they deflect differentially, they mainly control roll.

[0039] For example, three carbon fiber control surfaces can be equidistantly distributed along the trailing edge of the tail fin, with the central control surface 14 having a deflection range of ±30° and the lateral control surfaces 15 having a deflection range of ±25°. Unlike traditional yaw / roll and pitch controls which are independent, the two lateral control surfaces of this invention are significantly tilted due to their arc-shaped distribution along the trailing edge of the tail fin. Therefore, when one of the lateral control surfaces 15 is independently manipulated, the pitch and yaw actions of the aircraft can be simultaneously obtained. Thus, although the lateral control surfaces 15 are mainly used to control yaw and roll, the central control surface 14 also needs to be manipulated synchronously to suppress unnecessary pitch actions. For example, when the lateral control surfaces 15 are simultaneously deflected downwards or upwards, while controlling yaw, the tilted lateral control surfaces 15 will also produce pitch control actions on the airflow. To avoid unnecessary changes in pitch attitude during yaw, the central control surface 14 can be manipulated synchronously in the opposite direction to counteract unnecessary pitch.

[0040] Compared with the traditional T-tail, the semi-circular tail fin of this invention can significantly accelerate the airflow velocity along the curved surface and delay airflow separation. In wind tunnel tests at 200 km / h, the cruise drag of the tail fin of this invention (the horizontal distance from the highest point of the leading edge beyond the tail tip of the aircraft is 0.5 times the chord length of the tail airfoil section, and the leading edge sweep angle is 25 degrees) can be reduced by 15%. In addition, the semi-circular tail fin of this invention can still maintain stable control at high angles of attack (α=25°), while the traditional T-tail fin enters a rudder failure state when α>20°. The average stall angle of attack can be increased by about 8 degrees compared with the traditional tail fin structure (based on CFD turbulent kinetic energy analysis). Experimental verification shows that the control surface efficiency of the yaw-roll decoupled control of this invention can be improved by up to 2 times compared with US 5242132 A, especially at high angles of attack (α=25°), the pitch moment coefficient can be increased from 0.08 to 0.16, and the crosswind landing accuracy is improved by more than 30% (1000 Monte Carlo simulations).

[0041] Furthermore, because the semi-circular tail fin of this invention avoids the tail structure of the fuselage, it prevents slipstream impact vibration and improves the fatigue life of the tail fin structure. For example, through 2000 hours of bench vibration testing, the fatigue life of the tail fin structure of this invention is on average 2.5 times higher than that of the traditional T-tail fin. Simultaneously, comparative experiments show that the tail fin of this invention (with the highest point of the leading edge extending 0.8 times the chord length of the tail airfoil section beyond the aircraft's tail tip, and a leading edge sweep angle of 50 degrees) reduces noise by 7 dB (FAR 36 standard measurement point) compared to US6592073 B1 due to the avoidance of ducted flow interference. Regarding tail fin maintainability, the open structure of the tail fin of this invention reduces engine replacement maintenance time from 4 hours to 1.5 hours compared to the traditional T-tail fin.

[0042] Overall, the semi-annular tail fin of this invention can accelerate airflow speed in terms of aerodynamic efficiency. For example, the highest point of the leading edge of the semi-annular tail fin extends 0.7 times the chord length of the tail airfoil section beyond the tail tip of the aircraft. When the leading edge sweep angle is 35 degrees, the boundary layer separation point is delayed to 85% of the chord length (verified by infrared thermal imaging). The lift-to-drag ratio is improved to 9.2 compared to the traditional T-tail fin (7.1 improvement compared to the traditional tail fin). The open structure of the annular tail fin of this invention shows in ballistic impact tests that local damage only leads to the failure of a single control surface (in contrast, the annular tail fin of WO 2008 / 081098 A1 showed overall instability). Redundant control surfaces can maintain controllable flight, and the structure can reduce weight by up to 15% compared to the B737-800 avionics simulator structure, while improving fuel efficiency by more than 12%.

[0043] Compared with the prior art, the semi-annular tail aircraft of the present invention has the following beneficial effects: (1) Significant weight reduction. The semi-annular open structure eliminates the lower closed frame, and the structural mass is reduced compared with the annular tail or the all-moving arc tail, while maintaining sufficient rigidity and aerodynamic stability. (2) Reduced aerodynamic interference. The connection area of ​​the semi-annular tail is located below the wing, and the high-speed airflow on the upper surface of the fuselage can avoid the connection area, reducing aerodynamic interference and improving airflow adhesion. (3) Improved handling performance. The lower open structure and swept arc layout allow the tail rudder surface to avoid obstruction by the tail of the fuselage at high angles of attack, maintaining effective airflow and preventing rudder effect attenuation or control failure at high angles of attack. (4) Enhanced maintainability. The lower open structure provides more accessible space for the fuselage and tail propulsion device below the tail, improving the maintainability and maintenance efficiency of the tail structure and power system.

[0044] As described in the background section, existing vertical takeoff and landing (VTOL) aircraft, such as those disclosed in CN 114852324 B, suffer from insufficient lift and a sudden drop in lift during state transitions. Furthermore, conventional tail fin designs lack coupling with the propeller, causing interference between the tail fin and the propeller. Therefore, this invention, based on an improved semi-circular tail fin, further proposes a lift-coupled propulsion structure for semi-circular tail fin aircraft, such as... Figure 3-8 As shown.

[0045] As shown in the figure, the present invention adopts a blended wing-body structure. The semi-annular tail fin 1 forms a stable horizontal airflow suction on the upper surface of the blended wing-body. In order to avoid aerodynamic separation of the lift propeller 5 under the action of the horizontal airflow, the present invention sets the lift propeller 5 at the front and rear ends of the connecting rod 13 under the wing. The lift propeller 5 is installed downward on the lower side of the connecting rod 13, so that the propeller disk surface of the lift propeller 5 is far away from the upper surface of the blended wing-body, thereby partially mitigating the influence of the horizontal airflow on the upper surface on the lift.

[0046] To further reduce the impact of the upper surface airflow on the lift propeller 5, the present invention designs a coupling region between the lift propeller 5 and the wing-body blending body. By shielding the rotational profile of the lift propeller 5, which is most affected by the wing-body, under the fuselage and wing, the propeller tip is shielded to weaken the tip vortex and further reduce lift loss.

[0047] Specifically, such as Figure 3 As shown, the maximum angle α between the rotational profile of the lift propeller 5 at the front end of the connecting rod 13 and the outer profile of the forward fuselage on the vertical projection plane, relative to the rotation center of the lift propeller 5, is 45±5 degrees; the maximum angle β between the rotational profile of the lift propeller 5 at the rear end of the connecting rod 13 and the outer profiles of the rear fuselage and the trailing edge of the wing on the vertical projection plane, relative to the rotation center of the lift propeller 5, is 90±5 degrees. Wind tunnel experiments show that, under the same conditions, when the lift-coupled propulsion structure of the present invention has a relatively small shielding area, it can increase lift by more than 12% during vertical takeoff and landing; while when the relatively large shielding area is, the present invention can increase lift by more than 16% during vertical takeoff and landing.

[0048] To avoid the impact of horizontal airflow on lift on the upper surface of the wing, it is necessary to enhance the airflow suction capability of the lift propeller 5 on the upper surface, improve the lift propeller's ability to suction the wake turbulence in the wing-body blending zone during the transition from vertical takeoff to horizontal cruise, compensate for the drone's lift, and delay the lift change time. The lift-coupled propulsion structure of this invention further sets the installation angle γ of the lift propeller 5 to be tilted inward by 3-5 degrees relative to the longitudinal vertical plane of the fuselage, such as... Figure 4 As shown. Experiments show that tilting the installation angle γ inward by 3-5 degrees can extend the time of sudden drop in lift by about 10% compared to not tilting at all during the transition phase. Of course, if the inward tilt angle is too large, it will cause the horizontal component of the lift to be canceled out, reducing the efficiency of the lift propeller.

[0049] Furthermore, although the distance between the rotor disk of lift propeller 5 and the upper surface of the blended wing-body has some benefit in mitigating the impact of horizontal airflow on lift, the distance between the rotor disk of lift propeller 5 and the fuselage centerline is too large. During level flight, this will create a significant deflection moment with the thrust of propeller 6, leading to a reduction in the coupling efficiency between the semi-annular tail fin 1 and lift propeller 5. Therefore, as... Figure 5-6 As shown, the lift-coupled propulsion structure of the present invention further specifies that the minimum vertical height between the disk surface of the lift propeller 5 located at the front end of the connecting rod 13 and the lip line of the forward fuselage is H1, where H1 < R / 4, and R is the diameter of the lift propeller 5. Furthermore, the lift-coupled propulsion structure of the present invention further specifies that the minimum vertical height between the disk surface of the lift propeller 5 located at the rear end of the connecting rod 13 and the trailing edge of the wing is H2, where H1 < R / 4, and R is also the diameter of the lift propeller 5.

[0050] Furthermore, as mentioned above, in Figure 7 In the lift-coupled propulsion structure shown, the horizontal distance C1 between the highest point of the leading edge of the semi-annular tail fin and the end of the aircraft tail section is 0.5-0.8 times the chord length C0 of the tail fin airfoil section. Since the propulsion propeller 3 is located at the tail of the fuselage, the end of the aircraft tail section is actually the end of the mounting structure of the propulsion propeller 3. In this embodiment, the coupling structure sets the propulsion propeller 3 entirely at the front end of the semi-annular tail fin 1, but the distance between the semi-annular tail fin 1 and the propulsion propeller 3 is limited to 0.5-0.8 times the chord length C0 of the tail fin airfoil section. Thus, higher propulsion efficiency can be obtained through the coupling of the semi-annular tail fin and the propulsion propeller. For example, previous case data show that when the horizontal distance C1 between the highest point of the leading edge and the tip of the aircraft's tail is 0.5 times the chord length C0 of the tail airfoil section, cruise drag can be reduced by 15%, and the stall angle of attack can be increased by about 8 degrees, etc.; when the horizontal distance C1 between the highest point of the leading edge and the tip of the aircraft's tail is 0.8 times the chord length C0 of the tail airfoil section, noise is reduced by 7 dB, and maintenance time is reduced from 4 hours to 1.5 hours, etc.; when the horizontal distance C1 between the highest point of the leading edge and the tip of the aircraft's tail is 0.7 times the chord length C0 of the tail airfoil section, weight reduction can reach 15%, and fuel efficiency can be improved by more than 12%, etc.

[0051] In one specific embodiment, such as Figure 8 As shown in the rear-view schematic structure of the aircraft tail, the highest point of the leading edge of the semi-annular tail fin 1 is located in the vertical plane of the fuselage longitudinal axis. The minimum vertical height L between the highest point of the leading edge of the semi-annular tail fin 1 and the tip of the propeller 3 is equal to 0.1-0.2 times the tip radius R of the propeller 3. In the coupled design structure of this invention, in addition to considering the interference problem, an optimal gap is specifically set between the tip of the propeller 3 and the semi-annular tail fin 1. Wind tunnel tests have shown that when the minimum vertical height L between the two is limited to within the range of 0.1-0.2 times the tip radius R of the propeller 3, the propulsion efficiency of the propeller 3 can be enhanced by the semi-annular tail fin 1. In one specific embodiment, under the same conditions, the optimized gap range of the present invention can improve propulsion efficiency by 10-15% compared to a conventional tail fin. When the minimum vertical height L is greater than 0.1-0.2 times the tip radius R of the propeller, the semi-annular tail fin 1 has almost the same effect as a conventional tail fin and does not substantially improve the propulsion efficiency of the propeller 3. When the minimum vertical height L is less than 0.1-0.2 times the tip radius R of the propeller 3, the impact of the airflow on the sidewall of the semi-annular tail fin 1 on the tip of the propeller 3 increases significantly, the tip noise is significantly enhanced, and it is not suitable for the normal operation of the propeller 3.

[0052] Furthermore, such as Figure 8As shown in the schematic diagram comparing the horizontal projection relationship between the rear and side views of the lift-coupled propulsion structure of the present invention, the radius at a position 0.6-0.7 times the tip radius R of the propeller 3 is set as R1. The intersection of the vertical highest point of the tip radius R with the horizontal projection of the leading edge 12 of the semi-annular tail fin 1 is P1. The intersection of the vertical highest point of radius R1 with the horizontal projection of the leading edge 12 of the semi-annular tail fin 1 is P2. The distance from the disk surface of the propeller 3 to point P1 is D1, and the distance from the disk surface of the propeller 3 to point P2 is D2. The difference between D2 and D1 is equal to 0.1-0.5 times the radius R. Since the leading edge 12 of the semi-annular tail fin has a swept-back configuration, D2 is obviously larger than D1. Figure 8 As shown.

[0053] Furthermore, theoretically, the closer the blades of propeller 3 are to the shaft, the lower their propulsion efficiency. Conventionally, the region within a radius of 0.6-0.7 times the tip radius R of propeller 3, where the blades are close to the shaft, is considered an inefficient propulsion zone. This means the propulsion efficiency of propeller 3 within radius R1 is relatively small. Therefore, in another coupling design structure of this invention, the region from radius R1 to radius R is defined as the efficient propulsion region of propeller 3. Projecting this region horizontally onto the leading edge 12 of the semi-annular tail fin 1 yields a leading-edge efficient coupling region between points P1 and P2, corresponding to the efficient propulsion region of propeller 3. Research has found that distances D1 and D2 between the leading-edge efficient coupling region between points P1 and P2 and the propeller disk surface of propeller 3, under specific structural conditions, can achieve higher propulsion efficiency. Studies show that when the difference between D2 and D1 is equal to 0.1-0.5 times the radius R, the propulsion efficiency can be increased by 12%-16%. Under the same conditions, when the difference between D2 and D1 is greater than 0.1-0.5 times the radius R, the semi-annular tail fin of the present invention is similar to that of a conventional tail fin and has almost no impact on propulsion efficiency; when the difference between D2 and D1 is less than 0.1-0.5 times the radius R, the semi-annular tail fin of the present invention will significantly reduce propulsion efficiency.

[0054] In summary, this invention proposes a lift-coupled propulsion structure specifically for a semi-annular tail fin. By optimizing the coupling relationship between the propulsion propeller and the semi-annular tail fin, as well as between the lift propeller and the fuselage / wing, the propulsion efficiency of the propeller can be significantly improved, the lift loss of the lift propeller can be reduced, and the time of sudden lift drop can be delayed, while leveraging the structural advantages of the semi-annular tail fin. For example, by setting the propeller as a whole at the leading edge of the semi-annular tail fin, and limiting the distance of the semi-annular tail fin beyond the propeller propeller to a certain range, higher propulsion efficiency can be obtained. By designing a coupling region between the lift propeller and the blended wing-body, the rotational profile of the lift propeller, which is most affected by the wing-body, is shielded below the fuselage and wing, thereby shielding the propeller tip to weaken the tip vortex and further reduce lift loss.

[0055] Those skilled in the art should understand that although the present invention has been described with reference to multiple embodiments, not every embodiment contains only one independent technical solution. This description is provided merely for clarity; those skilled in the art should understand the specification as a whole and consider the technical solutions involved in each embodiment as being able to be combined with each other to form different embodiments to understand the scope of protection of the present invention.

[0056] The above description is merely an illustrative embodiment of the present invention and is not intended to limit the scope of the invention. Any equivalent changes, modifications, and combinations made by those skilled in the art without departing from the concept and principles of the present invention should fall within the scope of protection of the present invention.

Claims

1. A lift-coupled propulsion structure for a semi-annular tail fin aircraft, the semi-annular tail fin aircraft comprising a fuselage, wings, and a propeller (3) located at the tail end of the fuselage, wherein a connecting rod (13) parallel to the axis of the fuselage is provided below each wing on both sides of the fuselage, and a lift propeller (5) is provided at each of the front and rear ends of the connecting rod (13); characterized in that, The rear ends of the two connecting rods (13) are connected to a semi-annular tail fin (1). The semi-annular tail fin (1) starts from the rear end of the connecting rods (13) and extends upward along an arc path to form a semi-annular aerodynamic structure with the opening facing downward. The highest point of the leading edge of the semi-annular tail fin (1) is located in the vertical plane of the fuselage longitudinal axis. The minimum vertical height L of the highest point of the leading edge of the semi-annular tail fin (1) from the tip of the propeller (3) is equal to 0 times the tip radius R of the propeller (3). 1-0.2 times; the maximum angle α between the rotational profile of the lifting propeller (5) at the front end of the connecting rod (13) and the outer profile of the front fuselage on the vertical projection plane is 45±5 degrees; the maximum angle β between the rotational profile of the lifting propeller (5) at the rear end of the connecting rod (13) and the outer profile of the rear fuselage and the trailing edge of the wing on the vertical projection plane is 90±5 degrees.

2. The lift-coupled propulsion structure as described in claim 1, characterized in that, The leading edge (12) of the semi-circular tail fin (1) is swept back, and the horizontal distance C1 at which the highest point of the leading edge of the semi-circular tail fin (1) exceeds the end of the aircraft tail is equal to 0.5-0.8 times the chord length C0 of the tail airfoil section.

3. The lift-coupled propulsion structure as described in claim 1, characterized in that, The installation angle γ of the lifting propeller (5) is tilted inward by 3-5 degrees relative to the longitudinal vertical plane of the fuselage.

4. The lift-coupled propulsion structure as described in claim 1, characterized in that, The minimum vertical height between the disk surface of the lifting propeller (5) located at the front end of the connecting rod (13) and the lip line of the front fuselage is H1, where H1 < R / 4, and R is the diameter of the lifting propeller (5).

5. The lift-coupled propulsion structure as described in claim 1, characterized in that, The minimum vertical distance between the disk surface of the lifting propeller (5) located at the rear end of the connecting rod (13) and the trailing edge of the wing is H2, H1 < R / 4, where R is the diameter of the lifting propeller (5).

6. The lift-coupled propulsion structure as described in claim 1, characterized in that, The radius of the propeller (3) at a position 0.6-0.7 times the tip radius R is R1. The vertical highest point of the tip radius R is the intersection of the horizontal projection of the leading edge (12) of the semi-annular tail fin (1) with P1. The vertical highest point of the radius R1 is the intersection of the horizontal projection of the leading edge (12) of the semi-annular tail fin (1) with P2. The distance from the propeller disk surface of the propeller (3) to point P1 is D1. The distance from the propeller disk surface of the propeller (3) to point P2 is D2. The difference between D2 and D1 is equal to 0.1-0.5 times the radius R.

7. The lift-coupled propulsion structure as described in claim 1, characterized in that, The leading edge (12) of the semi-circular tail fin (1) has a sweep angle of 25-50 degrees relative to the horizontal plane passing through the longitudinal axis of the fuselage.

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